Cesium-Induced Stabilization of the FeOOH Cocatalyst on Bismuth Vanadate Photoanode for Ultraefficient and Stable Photoelectrochemical Water Oxidation

Developing active and durable water oxidation cocatalysts is essential for advancing photoelectrochemical (PEC) water-splitting systems. This study investigates the cesium-induced reconstruction of the FeOOH cocatalyst on a bismuth vanadate (BVO) photoanode for the water oxidation reaction, with a focus on the reconstruction process and its effect in improving interfacial charge transfer and photostability. Cesium ions induce the reconstruction of Fe species on the BVO/FeOOH photoanode during the PEC process, leading to the formation of a robust Cs-incorporated FeOOH (Cs:FeOOH) catalytic layer. Spectroscopic analysis combined with open-circuit potential measurement reveals that the in situ formed Cs:FeOOH cocatalyst can effectively protect BVO and promote interfacial hole transfer during PEC operation. As a result, the BVO/Cs:FeOOH photoanode achieves a photocurrent density of 6.29 mA cm–2 at 1.23 V vs. RHE and maintains stable operation for over 100 h. Furthermore, the Cs-incorporated FeOOH cocatalyst strategy can be extended to other semiconductor systems, including TiO2 and FeOx, highlighting its broader potential for improving solar-driven PEC water oxidation.